Photometers for performing analytical measurements are known. One such instrument is described in U.S. Pat. No. 3,704,953 (Carter et al.). The instrument shown in that patent includes a spectrophotometer that can be programmed to detect light of selected wavelengths. Samples to be analyzed are held in containers that have optically readable codes thereon. The instrument reads the code on the sample container as it is loaded into the spectrophotometer, the particular code being representative of the test to be conducted on that sample. The spectrophotometer then scans the wavelengths necessary to conduct the particular test and records the results.
Instruments of the type shown in the Carter patent are, typically, complicated laboratory instruments that are not easily carried into the field for use.